1. Field of Invention
The field of the present invention relates to multi-tone transceivers.
2. Description of the Related Art
Digital Subscriber Lines (DSL) technology and improvements thereon including: G.Lite, ADSL, ADSL2, ADSL2+, VDSL1, VDSL2, HDSL all of which are broadly identified as X-DSL have been developed to increase the effective bandwidth of existing subscriber line connections to high speed back bone networks developed by telecommunications companies. An X-DSL modem operates at frequencies higher than the voice band frequencies, thus an X-DSL modem may operate simultaneously with a voice band modem or a telephone conversation.
Each new XDSL protocol raises the bandwidth requirements of subscriber lines. As the bandwidth requirements increase so too does the complexity of the modem components. Additionally, because of the enormous variation in loop loss in the individual subscriber lines to which the modem may be coupled the individual components of the modem transmit and receive path must be reconfigurable to match the available bandwidth on a selected subscriber line.
Typically the central office (CO) of the telephone company includes racks of line cards each servicing many subscriber lines. Each line card includes many chips handling the digital and analog portions of the various XDSL communications over the subscriber lines. Each communication channel modulated onto a corresponding one of the digital subscriber lines is subject to crosstalk from communications channels modulated onto remaining ones of the digital subscriber lines in a bundle. This crosstalk degrades the performance of each digital subscriber line in a bundle of subscriber lines and in the extreme may render a given subscriber line connection inoperable.
What is needed is a modem with improved capabilities for responding to varying crosstalk levels in bundled digital subscriber lines.